Apparatus for photo etching

ABSTRACT

The exposure station of a photoresist pattern controlled continuous strip etching apparatus stores a movable, continuous loop photographic film transparency of the master pattern in lengths up to 50 feet or more for controlled contact photo printing of the pattern onto the resist coated moving strip which frictionally drives the same.

United States Patent [191 Crumley et a1.

APPARATUS FOR PHQIQ ELCI-IIIQIVG Filed:

Inventors: J. A. Crumley, James Ross Hildebrand, both of Camp Hill, Pa.; ljar ld Alfred lgerstetter, Shiremanstown, Pa.; Ray mfsiasr,

Lebanon, Pa.

Assignee: AMP Incorporated, Harrisburg, Pa.

Sept. 25, 1970 Appl. No.: 75,397

US. Cl. ..355/85, 355/90, 355/110,

Int. Cl. ..G03b 27/04 Field 01 Search....355/85, 89, 90, 104, 108, 109,

References Cited UNITED STATES PATENTS Serrurier ..352/l27 x Capstaff Frantzen Schwarz [4 1 Jan. 23, 1973 2,928,327 Blackmer et a1 ..355/104 UX 3,323,434 6/1967 Curtis ..355/90 3,479,120 11/1969 Davis..... 355/85 1,843,172 2/1932 Owens 355/90 1,725,944 8/1929 Thompson. ..355/90 2,041,478 5/1936 Niederle.... .....355/109 3,531,200 9/1970 Moll ..355/85 FOREIGN PATENTS OR APPLICATIONS 1,238,775 4/1967 Germany ..355l85 Primary Examiner-John M. Horan Assistant Examiner-Alan A. Mathews Attorney-Curtis, Morris and Safford, William J. Keating, Ronald D. Grefe, William Hintze, Adrian J. LaRue, Frederick W. Raring and Jay L. Seitchik [57] ABSTRACT The exposure station of a photoresist pattern controlled continuous strip etching apparatus stores a movable, continuous loop photographic film transparency of the master pattern in lengths up to 50 feet or more for controlled contact photo printing of the pattern onto the resist coated moving strip which frictionally drives the same.

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SHEET OSUF 10 fins PAIENTEDJMZIHQYS 3.712.735 sum 100F 1o APPARATUS FOR PHOTO ETCHING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the photo etching of continuously moving strip or web material and, more particularly, to the manufacture of uninterrupted printed circuits of lengths on the order of 50 feet or more on a flexible metalized web substrate or a thin metal web.

2. Description of the Prior Art One form of printed electrical circuits which are highly useful involves a thin flexible web of insulative material, such as Mylar or the like, which readily carries on one or'both sides, electrical conductors in the form of a configured conductive pattern for readily connecting multiple electric components at diversed, spaced locations along the web. Such flexible printed circuits have in the past been manufactured in a continuous photo etch facility, wherein a large roll of such metalized web material is continuously fed from a supply roll through the etching apparatus, and the completed circuit on the Mylar or other flexible substrate is then rewound onto a take-up roll at the opposite end of the processing machinery. During the movement, the metalized insulative film or substrate is uniformly coated with a photo resist material, which is then exposed photographically, to a film transparency or the like carrying the appropriate pattern of the circuit to be formed. The exposed resist material is then developed, which results in selective removal of the exposed material, allowing etching of the metal surfaces which remain uncoated by the resist prior to final removal of the' remaining unexposed resist.

The designation continuous photo etch is applicable, since the web is continuously moving through the facility and a repetitive circuit pattern is photographically transferred from transparencies to portions of the web during movement. Conventional photo etch facilities employ a step and repeat process incorporating a vacuum frame carrying the photographic master pattern in the form of the film transparency sheet of given size depending on the size of the vacuum frame. Necessarily, there is an accumulator both before and after the vacuum frame, whereby that portion of the web or strip being processed can be momentarily stopped and the pattern from the film transparency sheet is photographically transferred to the resist material on the strip or web by controlled exposure in conventional photographic fashion. In such an arrangement, the web is fed into the vacuum frame and it is stopped while the moving portion of the web downstream from the vacuum frame operates off the downstream accumulator. Meanwhile, vacuum is pulled to bring the transparency mask-into direct and intimate contact with the photosensitized material to expose the same to the pattern carried b'ythe film transparency. When the material is exposed, which takes several seconds, the exposed portion is removed by advancing the web the length of the vacuum frame, and another plate is exposed. With such a step and repeat process, the length of the printed circuit is necessarily strictly limited to the size of the vacuum frame. Thus, it has been impossible to photo etch continuous printed circuit in excess of about feet.

Some attempts have been made to correlate the adjacent portions of the strip being processed to different LII film transparencies or masks in attempt to extend the I length of the circuitry being processed through the continuous photo etch facility. Due to the close tolerances and small size of the individual circuit paths and the requirements for precision in registration of the succeeding portions of the composite circuit, attempts to increase the length of the circuitry manufactured by the step and repeat type continuous photo etch process, have been extremely disappointing.

SUMMARY OF THE INVENTION The present invention is directed to the utilization of one or more endless film transparencies of a length on the order of 50 feet or more, which bears a complete continuous master image of the desired pattern of circuitry to be etched which is stored in the exposure station of a continuous photo etch facility and moved into intimate contact with the web while moving to allow exposure of the same with the film driven thereby. Preferably, the film is supported in convoluted form on one side of the web for movement into overlying position therewith for photographically exposing the photo resist with the master-pattem carried by the film. Two such films may be provided, one on each side of the web for exposure of the photo resist on both sides of identical or different patterns under accurate registry. The convoluted film constitutes a continuous loop completely eliminating the step and repeat process or the necessity for accumulators. Racks having spaced, longitudinally offset but inter-engaging fingers extending from facing sides move toward and away from each other to allow initial introduction of the film, formation of the film loop and maintenance of the loop in convoluted form, for various loop lengths. The exposure station further includes a resilient pressure roll and a clear glass exposure roll which define an S-shaped path for the contacting portions of the film transparency loop and the photo resist coated web. The clear glass exposure roll carries internally, surrounding the light source, concentric metal sleeves having longitudinal slots. The sleeves may be rotated relative to each other to vary the aperture defined by the slots and thus the exposure time for the continuously moving web and film transparency. Preferably, the film transparency carries perforations along each edge with sprockets engaging the perforations and maintaining synchronization between the moving web and the frictionally driven film transparency. Drive means exterior of the exposure station coupled to the web moves the web through the photo etch facility and frictionally drives the master pattern film transparency. Registration between the film transparency and the web being processed is maintained by the frictional restraint of the overlapped film web about the peripheries of both rolls. A high intensity light source extends axially through the clear glass roll within the concentric metal sleeves, and two, concave curved tubes extend the length of the same between the light source and the internal sleeve, each curved tube extending approximately in circumference. Liquid coolant passes in ounterflow fashion through the tubes to effect uniform cooling of the light source and prevent destruction or detrimental thermal effects. to both the web being processed and each master film transparency loop.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the continuous photo etch facility in accordance with the present invention.

FIG. 2 is a front elevation of the exposure unit of the facility of FIG. 1.

FIG. 2A is an end elevation of one portion of the exposure unit shown in FIG. 2, illustrating the lower film transparency loop storage area.

FIG. 2B is a top plan sectional view of the storage area of FIG. 2A, taken about lines B--B.

FIG. 3 is a side elevational view of a portion of the unit of FIG. 2 taken along lines 3-3.

FIG. 4 is a sectional elevational view of a portion of the unit of FIG. 3 taken about lines 4-4, showing the exposure area and the associated structure.

FIG. 4A is a diagrammatic perspective view of the unit of FIG. 2 showing the master film threading paths.

FIG. 5 is an enlarged view taken along lines 5 S of FIG. 4, illustrating the synchronizing arrangement between the upper and lower film loops.

FIG. 6, 7 and 8 are sectional elevations taken along lines 6 6, 7 7, and 8 8, respectively of FIG. 3, showing progressively, portions of the unit of FIG. 2.

FIG. 9 is a perspective view, partially in section of the principal components of the glass roll defining the exposure means of the unit of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, as employed in the production of flexible printed circuits of extended length on the order of 50 feet or more, the web 1, which may constitute a copper-clad plastic material such as Mylar, is removed from a supply reel 2 in a continuous manner by positive drive means (not shown), which may be positioned at the take-up end of the machine or may be provided at intermediate points for ensuring controlled movement of the web 1 through the apparatus. The illustrated web 1 is slightly less than 2 feet in width and may be operated in conjunction with a splicer and accumulator (not shown), so that the machine is truly a continuous processing machine in which the leading end of a new web is merely spliced onto the trailing end of the old web without machine shut down. Alternatively, while the web 1 is described as a plastic substrate having a metal coating thereon, it could be simply a metal foil.

The web 1 first enters a scrub and rinse station 4 which may constitute a model No I000 spray etcher manufactured by the Chemcut Corporation. The unit 4 constitutes several elements and involves spraying of the web while moving horizontally with an alkaline solution on both sides thereof and which may incorporate a physical scrubbing apparatus such as the rotating brush. After treatment by an alkaline spray, the web moves into contact with a water rinsing unit and then an acid de-oxidizing unit, all forming components of unit 4. After acid de-oxidizing, the web next passes through a water rinse chamber. The web or strip 1 then passes through an air knife associated with the infra-red drying unit 6 to remove most of the water with infra-red heaters completely drying the same. Again, the infrared drying unit is conventional. The web 1 next passes to a photo resist coating unit 10, which may comprise a No. 765 coil coater manufactured by Gyrex Products/Varo Incorporated, constituting a roller coater for applying a liquid photosensitive resist to both sides of the metalized plastic web. The liquid photo resist is cured by passing the same through infra-red drying chambers identified at 12. The drying chambers constitute a solvent release cure with the surface temperature of the web being controlled by infra-red heat sensing elements. Dual infra-red heaters are employed, since the first set removes most of the solvent while the latter portion of the infra-red heater simply holds the temperature to just below the critical point of the breakdown of the materials, so that the release of solvent is complete, and thus the photo resist is fully cured prior to entering the exposure station 14.

The present invention is directed to the improved exposure station or unit 14 which exposes the photo resist photographically to the printed circuit pattern to be etched therein by apparatus downstream from the exposure unit. The exposure station orunit 14 will be described more fully hereinafter.

After exposure of the web, the web passes through the main S drive (not shown), which is preferably positioned just downstream of the exposure station or unit 14. The web next passes through a developing unit 20 which constitutes a dual tank unit that performs developing of the exposed resist material. The present facility is illustrated as a positiveresist system. Thus, the exposed resist washes off in the developer, leaving the circuit pattern of the unexposed resist. For example, the developing station 20 may constitute a Chemcut Model No. 1700 unit, the web leaving the developing unit and passing next to a rinsing unit 22. Here a water rinse is supplied, the web leaving the water rinse and entering the etching and rinsing station 24. With respect to the etching unit 24, this constitutes a dual chamber. That is, it is provided with two etch chambers in series, one of which may be operated exclusive of the other to provide varying etch times for the same speed of web passing through the facility, depending on the various thicknesses of metal being etched. Inthe etching unit, all of the treatment solutions are sprayed from both the top and bottom onto the horizontally moving web, with the treatment solutions being recirculated. This etching unit may constitute a Chemcut Model No. 568 etching unit of conventional design. With respect to the etching unit, the recirculated etching solution using a positive resist material, constitutes cupric chloride solution, which is regenerable. As the solution acts on the web, it reacts with the copper to dissolve the cooper away and forms cuprous chloride from the cupric chloride. This solution is then pumped out of the unit through a photo cell which photometrically reads the copper and determines'the amount of copper which has degenerated into cuprous chloride.'This unit adds chlorine gas automatically to the solution, which again re-oxidizes the cuprous chloride and returns the same to cupric chloride for recirculation. If the solution becomes too strong, water is added to redilute the solution to maintain a constant density. When volume increases beyond the holding capacity of the storage tank, it overflows and is pumped into a separate storage tank to be sold as a byproduct material resulting from the etching. By these means, a uniform etching solution is constantly maintained, and a uniform etching rate for a given speed of travel of the web through the facility.

The etched web next passes from the etching unit 24 to the triple rinse unit 25. In this unit, which constitutes a cascade type of rinse, fresh water is added to the last rinse, recirculated to the second and back to the first rinse. Alternatively, the liquid from the first rinse may be recirculated back into unit 22, which constitutes the rinse for the developing solution prior to the web entering the etch unit 24. This serves the dual purpose of helping to neutralize the alkaline solution and to maintain uniformity of cupric chloride solution through the elimination of drag-out of the alkaline solution into the etch chamber.

After the triple'rinse unit rinse in unit 25, the web passes through an infra-red drying unit which incorporates an air knife at its entry so that the web enters the re-exposure unit 26 in dry condition. The re-exposure unit 26 constitutes a Chemcut Model No. 1800, commercially available unit, which by re-exposure, causes the remaining resist on the circuit pattern to become soluble in an alkaline solution. The re-exposed web passes from exposure unit 26 to the stripping unit 28, whereby a solution the same as the developing solution or another alkaline sodium hydroxide solution, is preferably sprayed on both sides of the web to remove the remaining resist. Downstream of the stripping solution, in unit 28, is provided a final water rinse and air knife drying apparatus, with the web then passing next into unit 30 which constitutes an infra-red drying unit to completely dry the web prior to rewinding of the web 1 on reel 32. It is important, when rewinding the web, to prevent the entrapment of moisture between the layers to ensure against subsequent corrosion.

All of the units of the photo etch facility, with the exception of the exposure unit 14, are commercially available, formno portion of the present invention, and will not be described further.

The present invention is directed to the exposure station or unit 14 and, in particular, to its facility to enable flexible printed circuits of extended length to be produced when acting in conjunction with the other units of the photo etch facility illustrated in FIG. 1.

Referring to FIGS. 2, 2A and 2B, the exposure unit 14 comprises a frame consisting of four metal uprights 34 coupled at the top and bottom by a plurality of horizontal bracing members 36. The frame therefor defines an intermediate exposure section or-portion 38 and two film storage units above and below the same, identified at 40 and 42, respectively. Both film storage units are substantially identical, so that only the lower unit 42 is described in detail.

The unit 42, for instance, comprises a pair of generally rectangular horizontally oriented roller supporting racks 44 and 46, the upper rack 44 being stationarily mounted to the exposure unit frame. The unit is provided with a pair of spaced apart, vertically fixed rods 48 carrying slidable bushings 49, which in turn are fixed to the lower roller rack 46 such that rack 46 moves vertically toward and away from the fixed upper rack 44. The rack 46 is defined by right angle end plate 47 and side plate 51. The racks 44 and 46 carry on opposite sides and integral with the side plates thereof a plurality of spaced fingers or extensions 50. The longitudinally offset and oppositely directed fingers 50 carry a like number of rollers 52 to which the continuous film transparency loop is reeved to facilitate the take-up and storage of the film in a minimum amount of space. Units 40 and 42 will readily accommodate film transparency master pattern loops from 6 feet to 50 feet in length with rack 46 moving upwardly on rods 48 to support shorter loops.

With respect to this movement, it is noted that four fixed pulleys 58 are provided at fixed locations on the exposure unit and cables 56 which in turn are coupled at one end to the longitudinal extremities of movable rack 46 at the other end are coupled to a ratcheted winch 54 via drums 55, allowing the distance between the racks 44 and 46 to be adjusted and the rack 46 locked in position to avoid putting undue strain on the film during movement of the same over the rollers and through the exposure station 38.

With respect to the lower film 18, it enters exposure unit 38 at 60 and exits at 62, while the upper film 16 enters at 64 and exits at 66. The work piece strip 1 enters the unit at the left hand or upstream side at 68 and exits at 70 on the downstream side. This arrangement is seen best by reference to FIGS. 4, 4A and 5. The exposure section 38 comprises laterally spaced, vertically oriented support plates 102, fixedly mounted within unit 14 by means of end brackets 103, which are in turn coupled directly to U-shaped channel members 105 extending transversely across unit 14 from front to rear. Extending transversely between support plates 102 are positioned for rotation, various sprocket drive rolls for the film, guide and idler rolls for the same, and a large pressure roll associated with each clear glass exposure roll and the like. The illustrated arrangement constitutes two sets of rolls for effecting exposure of the resist material on both sides of the coated web 1. Referring to FIG. 4, the upper film transparency l6, entering at 64, passes clockwise over a guide roll 72 and may carry spaced perforations 73, FIG. 5, along one or both edges, which perforation receive the projecting teeth 75 of sprocket 74, thereby effecting positive registration and drive of the film 16 with respect to the underlying web or strip 1 carrying the resist material and film 18. The film 16 is wrapped about one-half the periphery of the sprocket roll 74 prior to contacting the upper surface of web I, with the film 16 and the web 1 at its entry 68 being sandwiched between sprocket roll 74 and an underlying back-up roll 76. In this respect, the backup roll constitutes an idler and is spring biased towards sprocket roll 74 by spring 77. The upper film 16 and the strip 1, in moving through the exposure unit, are wrapped clockwise about the large diameter resilient roll 78, the film 16 and web 1 taking a Z or S path, by in turn being partly wrapped about the periphery of the large diameter resilient roll 78 and the clear glass exposure roll 80 and nipped in between the same as at 79. The contacting web and film portion leave the periphery of the resilient roll 78 and are maintained tightly wrapped about the periphery of the clear glass roll 80 for an arc in excess of prior to traveling up and away from the glass roll 80. In exiting therefrom, the film l6 and the underlying web 1 pass again between an idler roll 87 and an underlying sprocket roll 82 with the sprocket teeth 83 passing through the perforations 73 of the transparent film loop 16. However, in this respect, the sprocket 82 is common to both films, since the lower film loop 18 which enters the unit at 60 engages the sprocket 82 after first passing over guide roll 92. The teeth 83 of sprocket 82 pass through perforations 93, FIG. 5, of the lower film loop 18 and then through perforations 73 of the upper film loop 16. Not only are the film loops 16 and 18 frictionally driven by engagement with the moving web or strip 1, but synchronism is maintained between the film strips due to the common engagement of sprocket teeth 83 with the perforations of the individual film loops. The upper film strip 16, beyond the area of the common sprockets 82, makes contact with and is partially wrapped about guide roll 84 prior to exiting the exposure unit 38 at 66 for storage in upper storage unit 40.

From the above description, it is obvious that the film 16 meets strip 1 and is pressed against it for travel therewith from the area of the sprocket roll 74 to the point it leaves roll 84. The number and positioning of the various rolls with respect to the lower film loop 18 are identical but of course reversely oriented to those involved in the movement of upper film loop 16. The film 18 entering at 60 passes counterclockwise over guide roller 92, clockwise over the common sprocket roll 82, clockwise over the large glass roll 94, effecting exposure to the photo resist on the under surface of web 1, counterclockwise on the large resilient roll 96, defining in conjunction with roll 94 the S path for the overlapped webs, clockwise on sprocket roll 98 and counterclockwise on guide roll 100, whereby the film loop 18 exits at 62 for storage in convoluted form within storage unit 42 as previously described. The film 18 meets and is pressed against the underside of the strip 1 being processed when it leaves sprocket roll 82 until it engages sprocket roll 98. Exposure of the photo resist to the pattern carried by the film transparency 16 and 18 is carried out in identical manner for both portions of the unit and accurate registry between patterns on opposite sides of the metalized web is maintained.

The mechanics of journaling each of the rolls thus described is somewhat conventional, with all of the small guide and idler rolls being journaled on the inside of side plates 102. However, the large diameter pressure rolls 78 and 96 are journaled on the outside of plates 102, while the glass rolls 80 and 94 are journaled on secondary plates 104 as best seen in FIGS. 3 and 7. In each case, each roll rotates about its longitudinal axis and they are rotated frictionally by contact with either web I, film 16, film 18, or a combination of the same. The surfaces of rolls 76 and 78 are resilient to prevent slippage between the films driven by the web 1 and the web itself as the web moves through the exposure unit. The films are picked up and travel along with the driven web, with each film transparency carrying a photo mask. These films mask off the circuit areas which are not to be exposed to the light source and, as such, each mask is positive since the illustrated facility constitutes an auto-positive resist system.

Both rolls 80 and 94 are transparent, preferably transparent hollow glass tubes. Reference to glass roll 80, FIG. 4, indicates that the hollow glass roll 80 carries a pair of concentric metal tubes or sleeves 86 and 88 of lesser diameter within the same with the metal sleeves not rotating with the outer glass roll although they are relatively rotatable, within limits with respect to themselves. Each metal tube carries an elongated slot 81 extending circumferentially approximately 100, such that the incidence of the slots by rotary orientation of the tubes permits the light from an ultraviolet light source 90 within the tubes to travel through the glass roller 80, and obviously, through the overlying mask defined by the patterned film strip 16 onto the upper surface of the strip 1. The exposure time is readily varied by rotating tube 88 relative to tube 86, which, of course, reduces the width of the exposure aperture defined by slots 81, that is, the circumferential extent of the same and thus the time period of exposure for a given speed of movement of web through the unit.

FIG. 8 constitutes an enlarged front view of a portion of the unit 14, including the support plate 104 in which the tubes 86 and 88 are journaled for angular adjustability. The outside tube 86 is permanently secured by welding, for instance, of the same to a flange 120, which in turn is secured by fasteners 122 to the outermost side plate 124. Spacer blocks 126, FIG. 7, allow plate 124 to extend outwardly from side plate 104, FIG. 3. The inside tube 88 is welded to a second flange 128, which, in turn, is mounted for rotational movement with respect to flange 120 by means of a screw 130, which projects through slot 132. The angular movement of flange 128 relative to flange 120 causes relative movement between the tubes 86 and 88 to thereby vary the width of the opening defined by slots 81 which, in turn, controls the extent of the exposure time.

In order to provide frictional wrap of the overlapped film strip and web portions about the periphery of the clear glass rolls 80 and 96, spring biasing means are provided as best seen in FIG. 3 and FIG. 6. In this respect, bearing blocks 106 are mounted for horizontal movement, between fixed guides 107, block 106 having spring 108 sandwiched between one face thereof, and fixed brackets 109 and held in place by shaft 111, about which it is concentrically positioned.

With respect to the mounting of the rotatable clear glass rolls 80 and 94, it-is noted that the opposed plates, FIG. 6, are apertured at 105, while plates 10, FIG. 7, are apertured at 111 to allow projection of the clear glass rolls therethrough. Three radial bearings, 110, 112, and 114, properly position and support the clear glass roll 80 for rotation. In this respect, the radial bearings 110 and 112 are adjustably but rigidly mounted, the radial bearings comprising rotatable discs 113 mounted for pivoting on arm 115, the amount of I pivoting or angular position of the same being controlled by adjustable screw 117. The radial bearing 114 is also supported on pivotable arm 1 19 and comprises a similar disc 121, but in this case a compression spring 123 acts on the outer end of arm 119 to bias disc 121 into contact with the periphery of roll 80. In similar fashion, for roll 94, three radial bearings 110', 112' and 114' are provided. Turning to FIG. 3, it is noted that the glass rolls are prevented from shifting axially, that is, end to end, by abutment against bearings 116 and 118, FIG. 3, which bear against the ends of these rolls. Bearing 116 is stationary while bearing 118 is spring biased and structured similarly to the radial bearing 114, but, of course, acts on the end of glass'roll 80. Similar means are provided for glass roll 94. The biasihg of bearings 1 18 compensates for irregularities in the glass, as do the sets of radial bearings 110, 112, 114, etc.

Reference to FIGS. 6 and 7, further illustrate the manner of heat dissipation within the glass exposure rolls and 94. There is some criticality, in the temperature to which the resist is subjected, since if once raised to a given value, it is impossible to redissolve it. For instance, if the resist material comprises a conventional AZ resist, the critical temperature is on the order of 180 F., and it is necessary to maintain the temperature of the web beneath this value. Further, it is necessary to protect the film itself from an excessive temperature, since this would tend to destroy or deteriorate the film. There is a vast amount of heat generated in the mercury vapor lamp 90 for each of the rollers 80 and 94, so this heat must be dissipated. In the present invention, two means are provided for effectively dissipating this heat. The primary heat dissipation results from employing two hollow metal tubes 128 and 130 which are arcuate in configuration, FIG. 9, and which are closedat their ends and each fluid coupled at one end to a source of liquid coolant. Pipe 132 may constitute an inlet end as indicated by the arrow 131, and the liquid coolant moves the full length of the upper tube 128, passing out at the right hand of the assembly, FIG. 9. A second coolant inlet is at 133 for lower tube 130 for counterflow as indicated by arrow 134 and ultimate dischargeat the left hand end of the assembly by means (not shown). Each colling tube has its own inlet and outlet, with counterflow for even dissipation of heat across tube. It is noted that the metal tubes are fixedly positioned to the sides of the slots 81 formed in tubes 86, 88, defining aperture opening 91. Each of the curved liquid coolant carrying tubes 128 and 130 form approximately a 120 are, covering essentially that are between the aperture tubes 86 and 88 and the light source with the exception of the aperture opening 91 defined by slots 81. In addition, forced air may be circulated within the clear glass rolls 80 and 94 to further dissipate the heat generated by the mercury vapor lamps. Such air circulation may be achieved by use of a conventional fan or blower (not shown).

The operation of the exposure unit 14 is believed to be readily apparent from the above description of the components of the same. However, briefly, as the web or strip 1 being etched passes through the unit 14 after having a resist material applied evenly to both sides thereof. Movement of the strip or web 1 causes, by frictional engagement with film loops 16 and 18, movement of these film loops from the storage areas 40 and 42 into the exposure section 38 in a continuous manner with the driven sprocket rolls 74, 82, and 98, merely maintaining synchronization between the film loops 16, 18. Controlled exposure of the strip 1 on both sides to the patterns carried by the individual photographic transparency loops 16 and 18 is dependent upon the speed of movement of the web 1 and the size of the aperture created by the concentric tubes 86 and 88 internally of both glass rolls 80 and 94. A greater or lesser number of support rolls 52 may be used for both storage areas 40 and 42 and, of course, the outer racks 46 and 46' may be shifted relative to the innermost fixed rack of each storage area to accommodate continuous film transparency loops of different lengths, thus producing continuous printed circuits of 50 foot lengths or more or, where a repetitive pattern for a single circuit strip is desired, the length of the circuit is dependent only upon the length of the web 1 being processed. Further, it is noted, that with the sprocket holes at definite predetermined distances along the length of the film, registration in forming the two films and the buttcoupling of each film to itself to form each film loop 16 and 18 after interleaving on rolls 52, is easily achieved. The master film may be readily made in loop lengths in excess of 50 feet by the employment of a computer driven light head on a light table supporting an extended sheet of film. Essentially, what is accomplished is the conversion of a product drawing of the desired circuit into digitized programming, which in turn is transferred into computer language on a punched tape, which is then fed to the plotter and which, in turn, draws the circuit by a photo head operating directly on photosensitized film. By the use of the sprocketed film, a system of registration is achieved employing the film itself, which is affixed to the light table using the flat pattern of the sprocketed film holes with the pegs to align the sprocketed film on the same. One of the pegs is provided with a cross hairline, which is used as a datum point or zero point for alignment of the digital readout system and from this alignment of the registration marks occurs with the circuit diagram in perfect registration for the individual segments it must match by employment of the datum point of reference. Minor touch-ups are readily achieved at the butt points to eliminate the joint from causing an unwanted print line. Using the endless film loops of considerable length and a frictional drive means, web speeds of 16 inches per minute have been readily achieved. Optimum design parameters constituting 3 feet per minute are defined on the basis of the facility being capable of etching one ounce copper or a thickness of copper of one and one-third mills at a speed of 3 feet per minute. One limiting parameter is the exposure time. Obviously, proper exposure time could be achieved at higher speeds by increasing the arc or aperture created by the concentric cylinders. However, the larger the exposure slot and thus the distance about the cylindrical clear glass roller requiring overlapping wrap of the web and film transparency, the greater the possibility of causing relative movement between the master film and the web, thus reducing fidelity and preciseness in pattern dimension. Additional parameters are important to exposure time, such as the thickness of the copper and the temperature of the etching solution. A heavier coating of photo resist is required to properly protect the circuit pattern from breakdown of the resist at increased temperatures, the breakdown resulting in pinholing, which in undesirable since it materially affects the conductivity of the circuit formed.

What is claimed is:

1. An etching apparatus for etching a predetermined pattern on a resist coated metallized web, said apparatus comprising an exposure unit,

web feeding means for continuously feeding said web along a web feed path which extends through said exposure unit, an endless film transparency bearing the master image of the desired pattern which is to be etched on said web, I

storage means for storing said endless film transparency within said exposure unit, said storage means comprising a pair of racks positioned on one side of said web feed path, said racks being adjustably movable towards and away from each other, a plurality of fingers extending from each of said racks, said fingers extending parallel to each other and the fingers of one of said racks being offset relative to the fingers of said other rack, rollers carried in said fingers, said rollers supporting said film,

transparency feeding means for continuously feeding said transparency along a transparency feeding path which extends from said storage means to, and beside said web feeding path through an exposure zone, thence away from said web feeding path to said storage means, and

exposure means in said exposure zone for exposing said web through said transparency.

2. Apparatus as set forth in claim 1 wherein said exposure means comprises a pressure roll,

a clear glass exposure roll,

means for resiliently biasing said pressure roll against said exposure roll, said web feed path extending over said pressure roll, between said pressure roll and said exposure roll, and over said exposure roll.

3. Apparatus as set forth in claim 2, said film and said web having perforations along corresponding sides thereof, said apparatus further having sprocket roll means in engagement with said web,and said transparency with sprocket teeth on said sprocket roll means extending through said perforations to ensure proper registration of said transparency with said web.

4. Apparatus as set forth in claim 3, said sprocket roll means comprising a first sprocket roll located upstream, relative to the direction of feed of said web, from said pressure roll and said exposure roll, and a second sprocket roll located downstream from said pressure roll and said exposure roll.

5. Apparatus as set forth in claim 2, said exposure roll having a light source therein, a pair of concentric angularly and relatively rotatable sleeves surrounding said light source, slots in said sleeves to jointly define an exposure aperature.

6. Apparatus as set forth in claim 5, said exposure roll having therein hollow tubes extending parallel to the axis thereof between said sleeves and said light source, and means for directing liquid coolant to dissipate heat from said light source.

7. Apparatus for selectively exposing both sides of a continuous web, said web having a central layer of insulating material and having metallic foil on each side of said central layer, said layers being coated with resist material, said apparatus comprising:

first and second exposure rolls, said rolls each having a light source therein, said rolls being mounted on parallel spaced-apart axes, means for continuously rotating said rolls in opposite directions,

means for feeding said web along a web feeding path, said web feeding path extending adjacent to both of said rolls,

first and second endless film transparency storing means, said first endless film transparency storing means being on one side of said web feeding path and said second endless film transparency storing means being on the other side of said web feeding fir t t r ansparency feeding means for feeding a first transparency along a first transparency feeding path which extends from said first storing means towards said web feeding path, thence along said web feeding path and between said web feeding path and said first exposure roll, thence to said first storing means, 1

second transparency feeding means for feeding a second transparency along a second transparency feeding path which extends from said second storing means towards said web feeding path thence along said web feeding path and between said web feeding path and said second exposure roll, thence to said second storing means, and

registering means for precisely registering said first and second transparencies with said web whereby, elongated patterns are exposed on both sides of said web are precisely located with respect to each other.

8. Apparatus as set forth in claim 7, said first and second exposure rolls having external surfaces which are spaced apart, said web feeding path extending adjacent to said first exposure roll thence to said second exposure roll, then adjacent'to said second exposure roll, then from said second exposure roll, said registering means being between said first and second exposure rolls.

9. Apparatus as set forth in claim 8, said first transparency feeding path extending to said web feeding path at a location upstream relative to the direction of web feed, from said first exposure roll, and said first transparency feeding means extending to said first storing means at a location downstream from said registering means, said second transparency feeding path extending to said web feeding path at a location upstream from said registering means and extending from said web feeding path and to said storing means at a location downstreamfrom said second exposure roll.

10. Apparatus as set forth in claim 9 wherein said registering means comprises sprocket means having sprocketteeth extending through perforations in said web and in said first and second transparencies. 

1. An etching apparatus for etching a predetermined pattern on a resist coated metallized web, said apparatus comprising an exposure unit, web feeding means for continuously feeding said web along a web feed path which extends through said exposure unit, an endless film transparency bearing the master image of the desired pattern which is to be etched on said web, storage means for storing said endless film transparency within said exposure unit, said storage means compRising a pair of racks positioned on one side of said web feed path, said racks being adjustably movable towards and away from each other, a plurality of fingers extending from each of said racks, said fingers extending parallel to each other and the fingers of one of said racks being offset relative to the fingers of said other rack, rollers carried in said fingers, said rollers supporting said film, transparency feeding means for continuously feeding said transparency along a transparency feeding path which extends from said storage means to, and beside said web feeding path through an exposure zone, thence away from said web feeding path to said storage means, and exposure means in said exposure zone for exposing said web through said transparency.
 2. Apparatus as set forth in claim 1 wherein said exposure means comprises a pressure roll, a clear glass exposure roll, means for resiliently biasing said pressure roll against said exposure roll, said web feed path extending over said pressure roll, between said pressure roll and said exposure roll, and over said exposure roll.
 3. Apparatus as set forth in claim 2, said film and said web having perforations along corresponding sides thereof, said apparatus further having sprocket roll means in engagement with said web and said transparency with sprocket teeth on said sprocket roll means extending through said perforations to ensure proper registration of said transparency with said web.
 4. Apparatus as set forth in claim 3, said sprocket roll means comprising a first sprocket roll located upstream, relative to the direction of feed of said web, from said pressure roll and said exposure roll, and a second sprocket roll located downstream from said pressure roll and said exposure roll.
 5. Apparatus as set forth in claim 2, said exposure roll having a light source therein, a pair of concentric angularly and relatively rotatable sleeves surrounding said light source, slots in said sleeves to jointly define an exposure aperature.
 6. Apparatus as set forth in claim 5, said exposure roll having therein hollow tubes extending parallel to the axis thereof between said sleeves and said light source, and means for directing liquid coolant to dissipate heat from said light source.
 7. Apparatus for selectively exposing both sides of a continuous web, said web having a central layer of insulating material and having metallic foil on each side of said central layer, said layers being coated with resist material, said apparatus comprising: first and second exposure rolls, said rolls each having a light source therein, said rolls being mounted on parallel spaced-apart axes, means for continuously rotating said rolls in opposite directions, means for feeding said web along a web feeding path, said web feeding path extending adjacent to both of said rolls, first and second endless film transparency storing means, said first endless film transparency storing means being on one side of said web feeding path and said second endless film transparency storing means being on the other side of said web feeding path, first transparency feeding means for feeding a first transparency along a first transparency feeding path which extends from said first storing means towards said web feeding path, thence along said web feeding path and between said web feeding path and said first exposure roll, thence to said first storing means, second transparency feeding means for feeding a second transparency along a second transparency feeding path which extends from said second storing means towards said web feeding path thence along said web feeding path and between said web feeding path and said second exposure roll, thence to said second storing means, and registering means for precisely registering said first and second transparencies with said web whereby, elongated patterns are exposed on both sides of said web are precisely located with respect to each other.
 8. Apparatus as set Forth in claim 7, said first and second exposure rolls having external surfaces which are spaced apart, said web feeding path extending adjacent to said first exposure roll thence to said second exposure roll, then adjacent to said second exposure roll, then from said second exposure roll, said registering means being between said first and second exposure rolls.
 9. Apparatus as set forth in claim 8, said first transparency feeding path extending to said web feeding path at a location upstream relative to the direction of web feed, from said first exposure roll, and said first transparency feeding means extending to said first storing means at a location downstream from said registering means, said second transparency feeding path extending to said web feeding path at a location upstream from said registering means and extending from said web feeding path and to said storing means at a location downstream from said second exposure roll.
 10. Apparatus as set forth in claim 9 wherein said registering means comprises sprocket means having sprocket teeth extending through perforations in said web and in said first and second transparencies. 